docs: def _get_moment_tensor_from_ndk_string(self, ndk_string):
          """
          Reads the moment tensor from the ndk_string and returns an instance of
          the GCMTMomentTensor class.
          By default the ndk format uses the Up, South, East (USE) reference
          system.
          """
          moment_tensor = GCMTMomentTensor('USE')
          tensor_data = _read_moment_tensor_from_ndk_string(ndk_string, 'USE')
          moment_tensor.tensor = tensor_data[0]
          moment_tensor.tensor_sigma = tensor_data[1]
          moment_tensor.exponent = tensor_data[2]
          return moment_tensor